Low temperature selective catalytic reduction of NO over polyarylamide-based carbon fibres

摘要

Carbon fibres have been used for the low temperature selective catalytic reduction of NO with NH_3 at temperatures in the range 100-400 deg C. The carbon fibres were obtained by pyrolysis of polyarylamide fibres (Nomex and Kevlar) at temperatures of 700 deg C and 850 deg C. NO reduction degrees in the range 40-80% were achieved with the carbonised fibres. No significant improvement in NO reduction was found by activating the carbonised fibres. The Nomex-based carbon fibres show higher NO reduction degrees than Kevlar-based ones. The presence of oxygen enhances NO conversion, probably due to oxidation of NO to NO_2. The change in concentration of NO and NH_3 (at NH_3/NO>1) hardly affects NO conversion. A minimum in the variation of NO conversion with temperature was observed for both types of samples, being more marked for the Kevlar-based carbon fibres. At temperatures below 250 deg C, the presence of water exerts a significant inhibitory effect upon NO reduction. Low-density carbon fibre-based monoliths prepared by agglomeration of carbonised Nomex fibres were used for NO reduction and a similar performance to that of the carbonised fibres was found.